First of all, stop thinkign that theres not exist countermeasures to not get sniped by jesters, corsairs,jANUSes, rape trains,strats, gunships, TML. This guide has it.
Jesters: Scout, if seeing enmey jester prepare tons of stationary AA, dont go away from it.
Corsairs/Janus/rape trains: at 15 minutes you should be T2, build some T2 shields, you're safe now. Get some flaks to help you/your air players. Specially corsairs, if you didnt had any intel ever and didnt had shields, dodge rockets with your com till get somebody to help you (or bring inties, ASF)
Strategic bombers = Personal shields, T2/T3 shields, more of them. At late games you should shield your com, scince its the best time for snipes. SAMs can help abit, but still cant kill whole rape train. Had no shields, try to dodge bombs.
Gunships = shields, they dont like them. Get flaks. Dont put your com at open space far from shields. For T3 gunships prepare SAMs.
TML = TMD walls. Build as much as you can, especally if its cybran TML. Scouting is needed. Building lots of TMD for no reason is stupid mass waste. If you/your team dont know how to build scouts play with camera away, if you see yellow squares coming at ur com you'll mostly likely gonna get "Commander under attack" and explode next second if you dont move.
Telemazes:Personal shields saves lifes again for few seconds, get lots of T1 PD around you if someone is building tons of Pgens. Not sure if somebody is gonna sacrifice himself for killing somebody. The sheild can hold up some dmg till PD kills the mazer. If you have scouted him already teleporting get into T2 transport so when he teleports he will die for no reason here.
Post more things you get sniped with ill give you the answer.